Ruddy Norah, this thing’s quick, credulity heaped on its 0-60mph time of 4.4 seconds with every zealous press of the accelerator. This, the still current iteration of Jaguar’s flagship XJ saloon, has been knocking around since 2009 in design terms, but a horizon-chomping ‘R’ model was absent from the lineup until more recently. I know not everyone does, but I for one consider the XJ to be beautiful. As long as a canal boat and with sleek, sexy lines, it’s nothing short of arresting, especially in the flesh. The XJR is the muscular choice but isn’t festooned with garish spoilers and the like, resolutely remaining a stealthy ‘sleeper’ or ‘Q car’.

Verdict: Ridiculously brisk, an immensely fun, rewarding drive and a bargain alongside its rivals. Headroom isn’t the most generous, the ride can be firm at slow speeds and the interior feels slightly dated since the competition upped their game.Rating: 4.1/5

Look closely and the XJR is set apart from its siblings by sizeable red callipers, quad tailpipes, ‘supercharged’ bonnet vents and ‘R’ louvres, a front splitter and 20” alloys that look the size of manhole covers. I admire the retained spirit of Britishness, the XJ not having been bludgeoned into a homogenous lump like certain other brands’ cars have. Nothing’s perfect (not even Jamie Dornan – sorry, ladies) and if you were to perch on a stool and stare at the XJR with passionate pedantry, you may question various minutiae, but as an overall design, I think it looks splendid. It sounds like a facelift is on the cards, perhaps for later this year, but it’s likely to be very restrained.

The XJR shares the XF’s rotary gear selector, which is also seen in Range Rovers, but the air vents that rotate when the ignition is fired in the XF make way for minimalist, curvaceous chrome vents in the flagship feline. I feel this is a good decision, removing any potential for perceived cheesiness and sticking to a sophisticated look akin to Bentleys.

All things are relative and when you’ve got £100,000 or more to spend on a high-performance, luxury saloon, you can afford to be picky. Compared to the inside of more common and affordable cars, of course the XJR feels opulent. The snag for Jaguar, though, is that the opposition has caught up and in some cases overtaken them when it comes to perceived quality, technology and innovation. Compared to the latest Mercedes S-Class and Audi S8, certain elements of the XJR’s interior feel ever so slightly flimsy and the infotainment system is definitely long in the tooth, now. Having said that, even a Bentley’s interior can be criticised in places, some components having been taken straight from a VW.

The last time I drove a Jaguar XJ, it was a 5-litre XJ Supersport and the glovebox was trimmed in purple velvet, so I half expected to see red velvet in the XJR’s. Anyway, it still opens with a single touch or brush from one’s finger, courtesy of JaguarSense™ technology, which also turns the interior overhead console lights on and off. The ebony veneer looks very smart, red stitching hints at the car’s sporting intent, the start button has a pulsating backlight to mimic a heartbeat and ‘R’ appears in various places from the seats to the steering wheel, along with illuminated treadplates. Phosphor Blue ambient lighting reinforces the thoroughly modern vibe of the XJR’s interior compared to Jags of old, and JLR’s simply brilliant Dual View system allowing the passenger to enjoy digital TV with the wireless headphones is another welcome feature. Technology like Audi’s ‘MMI touch’ also induces smiles, though, so although this big cat still feels special, Jaguar can’t rest on its laurels.

If you’re a businessperson, celebrity, politician or aristocrat and spend considerable periods of time being chauffeured around in the back of cars, the XJR remains impressively comfortable and spacious, despite only being available in short wheelbase (SWB) form. Tables and electrically reclining airline seats are options left for non-‘R’ LWB XJs, so the XJR isn’t the go-to choice for people who frequently work on the move. If, however, your chauffeur has a heavy right foot and your schedule often requires being driven cross-country, the XJR would be a fine car to pick, as it’s so damn fun to drive. Actually, it’s such a hoot that you may well make your poor chauffeur redundant so you can get behind the wheel yourself.

This super-saloon is up there with the best, that’s for sure, the 5-litre V8 serving up 550bhp and 680Nm of torque, taking you to 60mph in 4.4 seconds if you dare, with an academic top speed limited to 174mph. If these stats don’t get you salivating, I don’t know what will – and they are every bit as intoxicating in real life as they sound on paper.

Using aluminium to the full, the XJR feels so wonderfully light, completely contrary to its whopping footprint. It’s around 150kg lighter than rivals like the S-Class and actually marginally lighter than an XFR-S – and to me feels faster in practice. Its intimidating length shrinks away as soon as you sit in it and it’s not in the slightest bit daunting to pilot through narrow streets or around tight bends with serious aplomb.

Although not ultimately as communicative as the Panamera GTS I drove a couple of years ago, the XJR’s steering is sharp, precise and certainly enough to mangle wads of satisfying driving out of it. As you would expect, it is stiffer than other XJs and this does have an impact on the ride quality at slower speeds, amplified by the 20” wheels. Don’t get me wrong, unlike some cars in which speedbumps feel like landmines and potholes seem more like portals to Australia, the XJR’s manners around town and on poor surfaces aren’t awful, but they are compromised. Boot it on a severely undulating country lane, though, and the ride is truly remarkable, exhilarating but never dangerous, goading you on to push it harder and harder.

I said the XFR-S’ exhaust is too quiet and feel the same about the XJR’s, but it is a luxury super-saloon, after all, and a mere dab of the throttle still results in a lovely V8 burble. Rear-wheel drive, remarkably light and with a madman of an engine, the XJR offers the best of both worlds. One minute it’s a hushed cruiser aside from some wind noise. The next minute, it’s an axe murderer. Think of Inspector Clouseau relaxing in a nice, hot bath, then suddenly being pounced on by Cato. You get the picture. The way the XJR accelerates is utterly ridiculous, the supercharged V8 launching you towards the horizon in a smooth, linear, lag-and-lump-free fashion. You barely even need to go near the accelerator pedal on a motorway slip road and you’re instantly going far faster than you should. In the XJR, it only ever feels like you’re doing half the speed you actually are. It’s bonkers and rather pointless, but I’m not complaining. Getting the back end out is formulaically simple and rewardingly good fun – but believe me, it bites, often at random, so the uninitiated may find this big cat a bit of a handful. Get it right, though, and it’s an absolute joy.

The 8-speed ZF automatic transmission is remarkably smooth and gear changes are barely discernible, partially making up for the firm low-speed ride when it comes to the matter of wafting. Like a lot of gearboxes these days, it’s clever and knows what you want to do, even letting you change your mind in a split second. The Twin-Solenoid Stop-Start system is also accommodating, in case you stop in stationary traffic but then suddenly decide there’s enough space to exploit the 680Nm torque to dart to the front of the queue.

Behind the scenes, the tuned damping and springs, Corner Recognition, active electronic differential and Dynamic Stability Control certainly seem to result in agile, nimble and responsive cornering, allowing less experienced drivers to exploit the firepower on offer, the optimum gear held in readiness for exiting each corner. I’ve not driven a rival Mercedes S63 AMG yet with its revered Magic Body Control system, but wonder if the overall car is worth around £40k more than the XJR.

If you’re buying the XJR through a business, it emits 270g CO2/km, for what it’s worth. The combined consumption quoted at 24.4mpg is entirely believable and we managed 530 miles out of just under two tanks’ worth, despite driving it very enthusiastically indeed for prolonged periods.

The Jaguar XJR is the hooligan of the bunch, combining reasonable luxury with the ability to hoon on demand, wafting business associates around during the week then letting you enjoy donuts for breakfast on a Sunday, if you catch my drift – another thing it’s good at. An Audi S8 is constructed much more solidly and, like the allegedly-better-handling AMG Mercedes S-Class, can be specified with loads more gadgets and other options, but they lack the XJR’s bewilderingly sharp throttle response. Our typically fully-loaded press car came to less than £100,000, making it the bargain of the bunch, too.